We report the first demonstration of a four-mode semiconductor optical amplifier (FM-SOA), with strategically
positioned quantum-well layers to provide modal-gain control with uniform electrical pumping. On-off gain of 11 dB
was demonstrated for all four modes (E<sub>11</sub>, E<sub>12</sub>, E<sub>21</sub> and E<sub>22</sub>). The difference in on-off gain among all four modes is less than 1 dB in the range of 2-11 dB without any deliberately pumping profile control. Particular challenges with FM-SOA
that must be overcome in comparison with traditional single mode SOA are discussed.